1. Field of the Invention
The present invention relates to a two-core parallel extra-fine coaxial cable having two parallel cores including inner conductors whose outer peripheries are coated with insulations, and more particularly, to a two-core parallel extra-fine coaxial cable having high shield effect and flexibility.
2. Prior Art
Generally, in a coaxial cable, in order to enhance the shield effect, a metal volume (shield volume) is increased using a technique in which an outer shield is formed into a braiding shield or double shield. The same is applied to the two-core parallel extra-fine coaxial cable having two parallel cores including inner conductors whose outer peripheries are coated with insulations.
An example of the two-core parallel extra-fine coaxial cable is a cable in which two cores are arranged in parallel, outer peripheries thereof are provided with braiding shield as outer shield, a composite tape formed with a copper deposition layer having a thickness of 0.1 xcexcm or more is wound around the outer periphery of the braiding shield such that the copper deposition layer comes on the side of the braiding shield.
When the cable is wired in a narrow space such as a hinge portion of a notebook personal computer, it is required that the cable has flexibility and a diameter of the cable is fine. Since a notebook personal computer of recent year is used in high frequency region of 10 MH2 or more, a two-core parallel extra-fine coaxial cable using a braiding shield having high shield effect is used as an outer shield is preferably employed.
In the case of the braiding shield, however, the flexibility of the cable is extremely poor because of the metal volume, there is a problem that a finished outer diameter of the cable is slightly thick.
To solve this problem, in the two-core parallel extra-fine coaxial cable, there is a method in which the braiding shield is changed into a transversely wound shield. That is, this is a method in which a plurality of shield strands are wound spirally around outer peripheries of two cores at a predetermined pitch.
However, when the outer shield is only the transversely wound shield, since a continuous slit exists between the shield strands, there is a problem that the shield effect is largely deteriorated.
Further, if the pitch of the transversely wound shield is large, the continuous slit becomes large, the shield effect is deteriorated, and if the transversely wound shield pitch is small, the slit becomes small but there is a problem that the kink is generated in the cable itself by tension of the shield strand when it is produced.
Thereupon, it is an object of the present invention to provide a two-core parallel extra-fine coaxial cable having high shield effect and having such a sufficient flexibility that the cable is wired in a narrow space.
The present invention has been accomplished to achieve the above object, and a first aspect of the invention provides a two-core parallel extra-fine coaxial cable comprising,
two parallel cores having inner conductors whose outer peripheries are coated with insulations,
a transversely wound shield provided around outer peripheries of the two cores,
a composite tape which comprises a plastic tape formed on its one surface with a metal deposition layer and which is wound around an outer periphery of the transversely wound shield such that the metal deposition layer comes on the side of the transversely wound shield, and
a jacket for coating an outer periphery of the composite tape.
According to a second aspect of the invention, in the first aspect, an outer diameter of the inner conductor of the core is about 0.13 mm or less, an outer diameter of the core is 0.45 mm or less, and an outer diameter of the cable when coated with the jacket is 1.0 mm or less.
According to a third aspect of the invention, in the first or second aspect, a transversely winding pitch of the transversely wound shield is set in accordance with the following equation:
10xe2x89xa6(transversely winding pitch)/{(outer diameter of one of said cores)xc3x972+(diameter of a transversely wound strand)}xe2x89xa620.
According to a fourth aspect of the invention, in any of the first to third aspects, the transversely wound shield is formed by winding 30 to 60 strands comprising any of a soft copper wire, a tinned soft copper wire and a silver plated copper alloy wire around the outer peripheries of the two parallel cores.
According to a fifth aspect of the invention, in any of the first to fourth aspects, a diameter of each of strands forming the transversely wound shield is about 0.03 mm.
According to a sixth aspect of the invention, in any of the first to fifth aspects, the metal deposition layer formed on the composite tape is made of silver or copper, and a thickness of the metal deposition layer is 0.1 xcexcm or more.
According to a seventh aspects of the invention, there is provided a two-core parallel extra-fine coaxial cable comprising,
two parallel cores having inner conductors whose outer peripheries are coated with insulations,
a transversely wound shield provided around outer peripheries of the two cores,
a composite tape which comprises a plastic tape formed on its opposite surfaces with metal deposition layers and which is wound around an outer periphery of the transversely wound shield such that the metal deposition layers come on the side of the transversely wound shield, and
a jacket for coating an outer periphery of the composite tape.
According to an eighth aspects of the invention, in the seventh aspect, an outer diameter of the inner conductor of the core is about 0.13 mm or less, an outer diameter of the core is 0.45 mm or less, and an outer diameter of the cable when coated with the jacket is 1.0 mm or less.
According to a ninth aspect of the invention, in the seven or eighth aspect, a transversly winding pitch of the transversly wound shield is set in accordance with the following equation:
10xe2x89xa6(transversly winding pitch)/{(outer diameter of one of said cores)xc3x972+(diameter of a transversly wound strand)}xe2x89xa620.
According to a tenth aspect of the invention, in any of the seventh to ninth aspects, the transversely wound shield is formed by winding 30 to 60 strands comprising any of a soft copper wire, a tinned soft copper wire and a silver plated copper alloy wire around the outer peripheries of the two parallel cores.
According to an eleventh aspect of the invention, in any of the seventh to tenth aspects, a diameter of each of strands forming the transversely wound shield is about 0.03 mm.
According to a twelfth aspect of the invention, in any of the seventh to eleventh aspects, the metal deposition layer formed on the composite tape is made of silver or copper, and a thickness of the metal deposition layer is 0.1 xcexcm or more.